Rangelands provide important ecosystem services, including the sequestration of carbon, cycling of nutrients, and interception of runoff. Ecosystem services offered by rangelands depend on the health of their soils and can be measured by their capacity to support diverse plant communities and soil food webs. In this research we test whether soil nematodes can be used as indicators of soil health in wet meadow rangelands that have experienced different grazing regimes. Soil nematodes are sensitive to environmental changes and have evolved feeding strategies that allow them to specialize in the consumption of plant roots, fungal hyphae, bacteria, or other soil fauna. We compared trends in the plant community and soil to soil nematodes collected along a long- term grazing experiment in Manitoba, Canada. We extracted, counted, and assigned nematode genera to feeding groups to determine how grazing has affected the structure of the soil food web. We measured morphometric traits (length, volume, mass) of nematodes using digital images of individuals representing the dominant genera and collected the remaining traits related to metabolism and reproductive capacity from published literature. Using community weighted means of each trait, we hypothesized that: 1) smaller nematode genera will increase in abundance in soils more compacted by cattle grazing; and 2) the abundance of nematodes with more rapid metabolic activity and higher reproductive capacity will increase in areas enriched by nutrients through cattle grazing.
Results/Conclusions
Grazing had a significant effect on plant communities and soils. Early season, intense grazing decreased plant diversity and increased soil compaction. Although intense grazing increased the number of weedy species, late season, intense grazing also increased plant community richness and diversity. In contrast to our predictions, the length, volume, and mass of nematodes increased with grazing intensity. We observed a similar trend for the metabolic activity and reproductive capacity of soil nematodes. Timing of grazing had no effect on morphometric, metabolic, and reproductive traits of nematode communities. Our results suggest that intense grazing, combined with soil disturbance, contributes to higher turnover of soil resources that are reflected in the increasing size, metabolic, and reproductive capacity of soil nematodes. By exploring links between grazing and soil function, this research contributes new knowledge to understand the drivers of soil health in wet meadow rangelands. In collaboration with beef and forage producers in Manitoba, this research also provides a forum to exchange practical information and communicate ecosystem services provided by rangelands with the public.